U.S. Pat. No. 4,513,268 describes a residential circuit breaker employing a thermal-magnetic trip unit to interrupt circuit current upon the occurrence of an overcurrent condition. When an attempt is made to employ one such circuit breaker in a circuit in excess of the circuit breaker interruption capacity, the bimetal within the trip unit could become inoperably distorted and the circuit breaker contacts could become welded-together due to the intense heat and arcing generated during excessive short circuit overcurrent conditions.
U.S. Pat. No. 3,796,980 describes the inclusion of a separate fusible link between the circuit breaker flexible conductor and the bimetal to destroy the circuit breaker in the event that the bimetal becomes inoperative.
U.S. patent application Ser. No. 912,393 entitled "Thermal-Magnetic Trip Unit with Low Current Response" describes the advanced state-of-the-art of residential circuit breaker trip unit designs.
One purpose of the invention is to provide a fail-safe circuit breaker having low current response to insure that the circuit breaker trip unit responds to interrupt an associate electric circuit in the event that the trip unit bimetal becomes inoperative or the circuit breaker contacts become welded together in their closed condition.